If: $$ H (\pi(t)|\mu(t+1)) = \sum^n_{i=1}\pi_i(t) \log \frac{\pi_i(t)}{\mu_i(t+1)} $$
How do I interpret: $\nabla H(\pi(t) | \mu(t+1) )$?
Would it be the vector: $$ \left ( \frac{\partial H}{\partial \pi_1},.....,\frac{\partial H}{\partial \pi_n} \right) $$ or the scalar: $$ \frac{d}{d t}H $$